Physical–chemical treatment process optimization for high polluting dairy effluents prior fermentation

Among dairy effluents, bactofugate (B) and decreaming racking water (D) were identified as the most polluting due to their organic load content expressed in the chemical oxygen demand (156–240 g·L^?1). Joining the plant wastewater, such effluents contribute to the increase of the polluting load of the wastewater treatment plant input which disturbs the treatment performance. This work proposes an upstream segregation of those dairy effluents for combined physical–chemical and biological treatment. An experimental design was proposed to investigate initial pH, applied temperature and exposure time factor effects on the thermal coagulation process. The fermentation of the resulted supernatants using Lactobacillus lactis ssp. lactis was performed. The optimized thermal coagulation pretreatment was obtained at (pH; T(°C); t(min)): 6, 60 °C and 5 min, with both (B) and (D) effluents. Resulted clarified whey sugar, protein and fat contents were assessed. The physical–chemical treatment resulted in considerable organic matter removal: 45% for (B) samples and 31% for (D) samples of proteins content and almost the total fat content. However, there is no considerable effect on the sugar content reduction, which remains responsible for the major fraction of the whey residual chemical oxygen demand (COD). Clarified whey fermentation using Lactococcus lactis ssp. lactis strain induced important sugar consumption rates. Therefore, important sugar consumption rates were recorded and the COD removal efficiency was improved. The recorded global COD removal efficiency was of about 93%. The proposed combined physical–chemical and biological processes for dairy effluents pretreatment allowed not only to reduce the effluents polluting load, but also to valorize wheys by producing valuable components.     

Characterization of combined organic–inorganic acid-pretreated cassava stem

A number of previous studies established that the autoclave-mediated pretreatment enabled the efficient way of producing fermentable sugars from lignocellulosic residues. Hence, our emphasis was on studying the surface morphology of cassava stem to reveal its complex internal structure. In this study, combined organic (oxalic)–inorganic (sulfuric) acid was utilized for the pretreatment of cassava stem at 121 °C and 1 bar of pressure for 15 min. For the pretreatment, mixture containing 10 mL of 1% (w/v) of oxalic acid and 1% (w/v) sulfuric acid (5 mL each) was added to 1 g cassava stem and autoclaved. Pretreated samples were characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and ultraviolet spectroscopy (UVS). FTIR spectral studies confirmed the removal of hemicellulose and lignin from the pretreated cassava stem (PCS) when compared with untreated cassava stem. SEM micrographs revealed the decimation in the surface of cassava stem after pretreatment. XRD motifs shown that crystallinity index of PCS decreased from 63 to 52%. Thus, this study established the structural modifications to unlock its valuable components for further applications.     

Characterization of activated carbon obtained from Saudi Arabian fly ash

This study investigated the potential application of heavy oil burning fly ash as a precursor to prepare activated carbon. The raw fly ash obtained from a power plant is cleaned by nitric acid/hydrochloric acid and activated at 550–800 °C with hold times of 30 and 60 min to obtain fly ash activated carbon. The phosphoric acid is used as a chemical agent to improve the surface characteristics of the cleaned fly ash. The effects of process variables such as amount of chemical reagents, activation time and temperature were investigated according to two-levels full factorial design. The resultant activated carbons were characterized in terms of Brunauer, Emmett and Teller surface area and total and pore volume. The maximum specific surface area was found of 148.30 m²/g at 800 °C temperatures with 60 min holding time. The test showed that the surface area and pore volumes of the material are also significantly enhanced by the activation process.     

Lead and nickel biosorption with a fungal biomass isolated from metal mine drainage: Box–Behnken experimental design

The Pb(II) and Ni(II) biosorption of a fungal biomass isolated from mine drainage of metal-processing industries in Balya (Bal?kesir province, Turkey) was optimized using a response surface methodology by altering parameters such as pH, initial metal concentration, contact time and biosorbent dosage. This strain was shown to be highly similar to Penicillium sp. Furthermore, zeta potential measurements and Fourier transform infrared spectroscopy were performed to understand the adsorption mechanism. A Box–Behnken design with 29 experiments was used to evaluate the interactions between independent variables. The results showed that the fungal biomass isolated from the metal mine drainage could have a significant environmental impact through the biosorption of Pb(II) and Ni(II) in waters polluted with heavy metals, particularly in the drainage from metal mines. The maximum removal values were 76 and 47 % at pH 4.5 for both Pb(II) and Ni(II), with 123 and 33 mg/L initial metal concentrations, 65 and 89 min contact times and 0.2 and 1.6 g/L biosorbent, respectively.     

Simultaneous nitrification–denitrification of wastewater: effect of zeolite as a support in sequential batch reactor with step-feed strategy

One of the technologies used for wastewater nitrogen removal consists in simultaneous nitrification–denitrification. The low microbial growth rate and the low availability of organic material for the denitrification stage make it necessary to study new operational conditions and the use of microbial supports. The aim of this study was to evaluate the operational behavior of a simultaneous nitrification–denitrification process in a sequential batch reactor utilizing zeolite as a biomass support and step-feed strategy. Two reactors of 2 L were used, one with zeolite and another without zeolite, both operated at constant temperature (31 °C), varying nitrogen loading rate (NLR) from 0.041 to 0.113 kg total Kjeldahl nitrogen (TKN/m³/day). After 209 days, removals higher than 86 and 96 % in nitrogen compounds and organic matter were obtained, respectively. There was not accumulation of nitrate and nitrite in any case; this means that there was a simultaneous nitrification–denitrification in the reactors. The incorporation of zeolite in the system held higher concentration of biomass in the reactor; this led to reduce start-up to 21 days and to improve 11.31 % removal kinetic. The use of a step-feed strategy prevents events of inhibition by substrate, even duplicating tolerance to higher NLR for the same operation time.     

Optimization of parameters using response surface methodology and genetic algorithm for biological denitrification of wastewater

In the present study the removal of nitrates from wastewater using Pseudomonas stutzeri microorganism in a Gas–Liquid–Solid bioreactor at the concentration of 200 ppm was studied for a period of 12 h. The response surface methodology with the help of central composite design and genetic algorithm were employed to optimize the process parameters such as airflow rate, biofilm carrier, carbon source, temperature and pH which are responsible for the removal of nitrates. The optimized values of parameters found from RSM are airflow rate 2.41 lpm, biofilm carrier 15.15 g/L, carbon source 85.0 mg/L, temperature 29.74 °C, pH 7.47 and nitrate removal 193.16. The optimized parameters obtained from genetic algorithm are airflow rate 2.42 lpm, biofilm carrier 15.25 g/L, carbon source 84.98 mg/L, temperature 29.61 °C, pH 7.51 and nitrate removal is 194.14. The value of R² > 0.9831 obtained for the present mathematical model indicates the high correlation between observed and predicted values. The optimal values for nitrate removal at 200 ppm are suggested according to genetic algorithm and at these optimized parameters more than 96 % of nitrate removal was estimated, which meets the standards for drinking water.     

Utilization of palm oil mill effluent for polyhydroxyalkanoate production and nutrient removal using statistical design

The optimization for poly-β-hydroxyalkanoate production was carried out with nutrient removal efficiency for total organic carbon (TOC), phosphate, and nitrate from palm oil mill effluent waste. The experiment was conducted in a fabricated fed-batch reactor and the data obtained was analyzed using central composite rotatable design and factorial design for response surface methodology as a systematic approach for designing the experiment statistically to obtain valid results with minimum effort, time, and resources. The analysis of numerical optimization with propagation of error showed that 66 % of poly-β-hydroxyalkanoate production can be obtained with nutrient removal of TOC and nitrate by 19 and 3 %, respectively. However, phosphate removal efficiency was not found to be much effective. More over, the chemical oxygen demand: nitrogen phosphate (509 g/g N), chemical oxygen demand: phosphate (200 g/g P), air flow rate (0.59 L/min), substrate feeding rate (20 mL/min), and cycle length (20 h) were the optimized variables for maximum poly-β-hydroxyalkanoate production and nutrient removal.     

Microbiological degradation of phenol using two co-aggregating bacterial strains

Phenol biodegradation in an aerobic batch reactor was investigated using mixed two co-aggregating strains (Flavobacterium sp. and Acetobacter sp.). Response surface methodology by the Box–Behnken model was used to evaluate the optimal cell growth and phenol degradation conditions. The optimum temperature, pH value and inoculum size were found to be 33 °C, 6.06 and 13 %, respectively. In the conditions, phenol degradation rate and biomass were predicted to be 96.97 % and 410.78 mg/L within the range examined, respectively. Less toxic acetaldehyde, ethanol and acetic ether were identified as main intermediate products from the degraded samples using GC–MS. Substrate inhibition was calculated from experimental biomass growth and phenol degradation parameters using the Haldane equation. Kinetic parameters derived from nonlinear regression with correlation factors (R ²) were 0.9682 for phenol degradation and 0.9594 for biomass growth, respectively. The phenol concentration to avoid substrate inhibition was 278.17 mg/L.     

Response surface methodology (RSM) optimization approach for degradation of Direct Blue 71 dye using CuO–ZnO nanocomposite

The present study highlights the synthesis of CuO–ZnO nanocomposite via facile hydrothermal method at 150 °C and autogenous pressure. The structural and textural features of prepared composite material was characterized by several characterization techniques such as X-ray powder diffraction, Fourier transform infrared spectroscopy, Scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The optimized prepared nanocomposite was utilized for photocatalytic degradation of aromatic Direct Blue 71 dye (DB71) under natural sunlight conditions. The catalytic activity results by CuO–ZnO nanocomposite were observed to be higher than the reagent-grade zinc oxide under visible light conditions. The response surface methodology protocol (RSM) with central composite design was optimized by different photodegradation operational parameters such as pH, dye concentration, catalyst amount, and reaction time. The optimized RSM results demonstrated that a quadratic polynomial model was found suitable to define the relation between the photocatalytic activity and operational parameters. Moreover, the observed high R ² value (0.9786) confirms a strong evaluation of experimental data. To achieve maximum DB71 degradation, optimized condition was found at 177.13 min of contact time, 3.93 solution pH, and 24.34 mg/L of dye concentration with 1.85 g/L of catalyst dose The identical optimum conditions resulted maximum 89.58% DB71 degradation.     

Removal of phosphates from aqueous solution by sepiolite-nano zero valent iron composite optimization with response surface methodology

In this study, sepiolite-nano zero valent iron composite was synthesized and applied for its potential adsorption to remove phosphates from aqueous solution. This composite was characterized by different techniques. For optimization of independent parameters (pH = 3–9; initial phosphate concentration = 5–100 mg/L; adsorbent dosage = 0.2–1 g/L; and contact time = 5–100 min), response surface methodology based on central composite design was used. Adsorption isotherms and kinetic models were done under optimum conditions. The results indicated that maximum adsorption efficiency of 99.43 and 92% for synthetic solution and real surface water sample, respectively, were achieved at optimum conditions of pH 4.5, initial phosphate concentration of 25 mg/L, adsorbent dosage of 0.8 g/L, and 46.26 min contact time. The interaction between adsorbent and adsorbate is better described with the Freundlich isotherm (R ² = 0.9537), and the kinetic of adsorption process followed pseudo-second-order model. Electrostatic interaction was the major mechanisms of the removal of phosphates from aqueous solution. The findings of this study showed that there is an effective adsorbent for removal of phosphates from aqueous solutions.     

Optimization of sample preparation method of total sulphur measurement in mine tailings

A sample preparation method of total sulphur measurement of reactive mine tailings was optimized. The total sulphur was measured by inductively coupled plasma optical emission spectroscopy, and ultrasound technique was used for sample digestion. The optimization process was adopted by a combined approach of experimental design and response surface methodology. The digestion time, temperature and acid-oxidant combination (i.e. effect of H₂O₂ with a fixed amount of acid mixture) were investigated. A two-level and three-factor (2³) full factorial design of experiment was applied to identify the most significant factors, and a central composite design was used to optimize the digestion procedure. KZK-1, a sericite schist, was selected as the certified reference material. The optimum methodology at 95 % confidence level (P < 0.05) was identified to be 10 min of digestion at 77 °C, with a solution of 1 ml HNO₃:1 ml HCl:1.35 ml H₂O₂. This combination resulted in 100 % sulphur recovery. The investigated method was verified by X-ray diffraction analysis. The optimum digestion level was applied to a reactive mine tailings, which achieved satisfactory results with a percentage relative standard deviation < 3 %.     

Evaluation of tropical seaweeds as feedstock for bioethanol production

Limited resources of freshwater and decreasing fossil fuel resources are two main reasons to consider the ocean as a huge resource for producing food, feed, fertilizer and feedstock for fuel. In this study, twenty-nine tropical seaweeds (11 green, 10 red and 8 brown seaweeds) collected in Malaysia were assessed as potential feedstock for bioethanol production. Total carbohydrate content ranged from 12.16 to 71.22% dry weight (DW) with total reducing sugar content ranging from 5.17 to 34.12% DW. During hydrolysis using dilute sulphuric acid, the dominant fermentation inhibitors were 5-hydroxymethylfurfural and phenolic compounds. Overliming was found to reduce the content of fermentation inhibitors by up to 79%. The red seaweeds, Kappaphycus alvarezii (Doty) Doty ex P.C.Silva and Gracilaria manilaensis Yamamoto and Trono, were selected for optimization of saccharification and fermentation of the hydrolysate, because they had the highest carbohydrate contents and are commercially cultivated. The most suitable dilute acid conditions obtained in present study was sulphuric acid (2.5%, w v^?1) treatment at 121 °C for 40 min that produced 0.29 and 0.34 g g^?1 DW reducing sugar for K. alvarezii and G. manilaensis, respectively. Fermentation of the hydrolysates with Saccharomyces cerevisiae produced bioethanol yields of 20.90 g L^?1 (71.0% of theoretical yield) for K. alvarezii and 18.16 g L^?1 (67.9% theoretical yield) for G. manilaensis.     

Catalytic hydrothermal carbonization of invasive macrophyte Hornwort (<Emphasis Type="Italic">Ceratophyllum demersum</Emphasis>) for production of hydrochar: a potential biofuel

Biofuels are environment friendly and economical. First-generation biofuels are made from sugar, starch and vegetable oils, and have an impact on food security, while second generation biofuels are generated from plant or algal material and are greener and sustainable. The present work focused on lab-scale application of hydrothermal carbonization to convert aquatic weed Ceratophyllum demersum into a second-generation biofuel—hydrochar. Hydrothermal carbonization has been carried out with and without catalysts in a high-pressure reactor under subcritical temperatures 240–320 °C, residence times 10–40 min and biomass to water dilution ratios varying from 1:4 to 1:12. Under noncatalytic conditions higher heating value and energy density were highest, 24.11 MJ/kg and 1.64 respectively at temperature of 300 °C and residence time of 30 min. The calorific value of noncatalytic hydrochar was enhanced further, respectively, to 29.0, 27.5 and 26.48 MJ/kg by catalysts KOH, Na₂CO₃ and acetic acid. Catalytic hydrochar had H/C and O/C atomic ratios of same order as that of high-rank bituminous coal. Van Krevelen diagram indicated KOH to be better catalyst followed by Na₂CO₃ and acetic acid. Hydrochar yield of 38% obtained in noncatalytic hydrothermal carbonization decreased with catalysts in following order; acetic acid > Na₂CO₃ > KOH, however, energy density was enhanced in order KOH > Na₂CO₃ > acetic acid. The research can prove a way forward in the direction of meeting part of global energy demand. At the same time, the problem of secondary pollution caused by piling up and decay of aquatic weeds will also be addressed to.     

Optimization of operational parameters for ethanol production from Korean food waste leachate

Recently, research on the production of ethanol from waste has been accelerating for both ecological and economical reasons, primarily for its use as an alternative to petroleum based fuels. In this study, response surface methodology based 2³ -full factorial central composite design was employed to optimize the parameters of ethanol production from Korean food waste leachate. The reducing sugar concentration of the food waste leachate determined by the dinitrosalicylic acid method was 75 g/L. A second order polynomial model was developed to evaluate the quantitative effects of temperature, pH and reducing sugar concentration in order to find an optimum condition for the ethanol production from food waste leachate. From the experimental result, maximum ethanol concentration of 24.17 g/L was obtained at the optimum condition of temperature (38 °C), pH (5.45) and reducing sugar concentration (75 g/L). The experimental value (24.17 g/L) agreed very well with the predicted one (23.66 g/L), indicating the suitability of the model employed and the success of response surface methodology in optimizing the conditions of ethanol production from food waste leachate. Canonical analysis indicated that the stationary point was a saddle point for the ethanol yield. Despite being a waste, an ethanol yield of 0.32 g ethanol/g reducing sugar demonstrated the potential of food waste leachate as a promising biomass resource for the production of ethanol.     

Improvement of anaerobic biodegradability of organic fraction of municipal solid waste by mechanical and thermochemical pretreatments

The effect of particle size of the organic fraction of municipal solid waste on methane potentiel was investigated and tested at different substrate-to-inoculum ratios (0.1, 0.5 and 1.0). The highest methane yield was obtained with particle size fraction > 3 mm at S/I of 0.1. Thermo-alkali and thermo-acid methods were also tested as pretreatment to increase the organic matter solubilization and subsequently methane production. The results indicated that maximum variation (63.6%) of soluble chemical oxygen demand was obtained by thermo-acid method. Optimum conditions of thermo-alkali pretreatment were pH 10, time reaction of 30 min and temperature of 105 °C. Soluble chemical oxygen demand and reducing sugar variations reached, respectively, 40 and 69% under these conditions. The methane yield of untreated and thermochemical pretreated OFMSW was determined in batch condition. The highest methane yield (260.9 L/kg VS) was obtained with thermo-alkali pretreatment, which was 21% higher than that of raw substrate. This study may pave a new way for industrial application of dealing with the organic fraction of municipal solid waste.     

Improvement in nitrification through the use of natural zeolite: influence of the biomass concentration and inoculum source

A batch nitrification process was studied using synthetic wastewater as substrate and Chilean natural zeolite as biomass carrier at ambient temperatures (20 °C). Three groups of experiments were carried out: a first experimental set (I) with and without added zeolite using initial biomass concentrations of 1,000 and 2,000 mg VSS/L; a second set of experiments (II) with added zeolite and at the same initial biomass concentrations. In these two experimental sets, biomass from an activated sludge process located in an urban wastewater treatment plant at La Farfana, Santiago de Chile, was used as inoculum (1). Finally, a third set of experiments (III) was carried out with zeolite at an initial biomass concentration of 1,000 mg VSS/L using an inoculum derived from an activated sludge process treating wastewater from a paper mill (inoculum 2). Nitrifying biomass concentration values in the range of 13,000–18,800 mg VSS/L were achieved when initial biomass concentrations varied between 1,000 and 2,000 mg VSS/L. Inoculum (1) generated higher biomass concentrations than inoculum (2). Ammonium N removals higher than 70 % were obtained in experimental sets II and III when zeolite was used. For both initial biomass concentrations tested, an exponential biomass growth was observed up to the second day of operation, and a slight decrease was evident afterwards, achieving stationary values after 10–12 days of operation. The third experimental set (III) revealed that the highest N consumption took place between days 11 and 16 of digestion.     

Response surface methodology mediated optimization of Remazol Orange decolorization in plain distilled water by Pseudomonas aeruginosa BCH

The bacterium Pseudomonas aeruginosa BCH decolorized and degraded the sulphonated azo dye Remazol Orange in plain distilled water. The effects of different parameters, i.e. pH, temperature and cell mass concentration on the biodegradation of dye in aqueous phase was evaluated using response surface methodology. Optimization was carried out using three-level Box–Behnken design. Predicted values were found to be in good agreement with experimental values (R ² 0.9997 and pred R ² 0.9984), which indicated suitability of the employed model and the success of response surface methodology. Optimum dye decolorization was maximized and the favourable conditions were pH 7.43, temperature 29.39 °C and cell mass concentration 2.88 g l^?1, which resulted in 96.01 % decolorization within 5 h. It was validated from the predicted response (97.37 %). According to the analysis of variance results, the proposed model can be used to navigate the design space. 3D plot analysis disclosed the significant interaction between all three tested factors on decolorization process. The combinations of the three variables predicted during response surface methodology were confirmed through confirmatory experiments. Observations indicated that higher cell mass accelerated the decolorization process. Degradation of the dye was verified through high performance liquid chromatography analysis. Phytotoxicity studies carried out with dye and dye metabolites using Phaseolus mungo, Triticum aestivum and Sorghum vulgare indicated the detoxification of dye.     

Enhancement of nickel biosorption on fungal biomass by enzymatic and alkali pretreatments

Enzymatic and alkali pretreatments were employed to improve nickel biosorption capacity of Rhizomucor pusillus biomass. Pretreatment with 0.002–80 g l^?1 NaOH and 0.0001–0.1 Anson Unit (AU) g^?1 protease enhanced the biosorption capacity of fungal biomass. Increasing the concentration of NaOH from 0.002 to 5 g l^?1 improved nickel removal from 93.2 to 100.0 % while untreated biomass showed 64.6 % Ni(II) removal. Pretreatment with higher concentrations of NaOH, 5–80 g l^?1 resulted in nearly complete removal of nickel ions. Pretreatment of the biomass with 0.0001 AU g^?1 protease improved the nickel removal to over 91 %, while increasing the enzyme loading to 0.1 AU g^?1 improved the removal to 93 %. Untreated biomass removed 78.4, 63.0, and 96.3 % of chromium, copper, and lead ions, respectively, from a mixture solution of the ions. Respective metal removals were increased to 100, 98.9, and 100 % after pretreatment with 0.2 g l^?1 NaOH solution and to 87.8, 86.7, and 100 % after the enzymatic pretreatment with 0.1 AU g^?1 protease. Scanning electron microscopy analysis indicated that alkali and enzymatic pretreatments enhanced the porosity of the biomass. Furthermore, compositional analysis showed that both of the pretreatments removed a major part of fungal proteins (2.1–95.8 % removal). Glucosamine, N-acetyl glucosamine, and phosphates were the major ingredients of the pretreated biomass.     

Application of a novel definitive screening design to decolorization of an azo dye on boron-doped diamond electrodes

The electrochemical decolorization of the Reactive Violet 5 azo dye on a boron-doped diamond anode was used as a model process to test a novel definitive screening design (DSD). This method allows a dramatic reduction in the number of experiments needed to investigate those systems characterized by a large number of variables. In this study, the effect of nine quantitative parameters was investigated: initial dye concentration (60–120 mg L^?1), current density (100–500 A m^?2), NaCl concentration (5–20 mM), Na₂SO₄ concentration (35–65 mM), pH (3–11), temperature (20–45 °C), inter-electrode distance (0.5–3.5 cm), stirring rate (250–750 rpm) and electrolysis time (2–8 min). Analysis of DSD data showed that four out of the nine factors (initial dye concentration, current density, pH and electrolysis time) were statistically significant. These factors were retained for process characterization using a subsequent central composite design. Overall, the number of experiments was reduced from over 500 to only 41, thus confirming the validity of the proposed approach as a time-saving and efficient method.     

Adsorption kinetic studies for removal of methylene blue using activated carbon prepared from sugar beet pulp

Sugar beet pulp is an abundant, renewable and low-cost precursor for production of activated carbon. In the present study, sugar beet pulp based activated carbon was prepared by using phosphoric acid as activating agent for adsorption of methylene blue. The conditions of preparation process had a significant influence on the adsorption of methylene blue, and the optimal preparation conditions were obtained as follows: liquid-to-solid ratio of 5, temperature of 450 °C and phosphoric acid concentration of 3 mol/L. The properties of sugar beet pulp based activated carbon were characterized by nitrogen adsorption isotherm. The adsorption increases as the increase of contact time, adsorption temperature and pH, and initial concentration of methylene blue. Batch kinetic studies showed that an equilibrium time of 100 min was needed for the adsorption, and the adsorbance of methylene blue is 244.76 mg/g at equilibration. Kinetic models, Weber’s pore diffusion model and Boyd’s equation were applied to the experimental data to study the mechanism of adsorption and the controlled step. The results showed that the adsorption kinetics followed the pseudo-second-order type kinetic model, intraparticle diffusion was not the rate-limiting mechanism and adsorption process was controlled by film diffusion.